The present invention relates to a method for dispersing finely divided catalysts onto the surface of a particulate material. More particularly, it relates to an improved method for dispersing hydrated iron oxide onto the surface of carbonaceous material such as coal in a manner to permit effective catalytic activity at relatively low concentrations of iron.
Iron and other transition metals have been used as dispersed-phase catalysts in processes for the hydrogenation and the direct liquefaction of coal. One major advantage of dispersed-phase catalysts is the potential for once through use with high initial activity. Representative processes of this type are described in U.S. Pat. No. 3,775,286 to Mukherjee et al. and in various technical publications such as Mitra et al., "A Comparative Study on Deposited and Mixed Iron Oxide Catalysts for Hydrogenation of Coal", FUEL PROCESSING TECHNOLOGY, 8(1924) 283-291. In this prior work, hydrated iron oxide was precipitated from solution by the addition of ammonium hydroxide onto particulate coal in suspension. Loadings typically of about 1.9 weight percent iron (19,000 ppm) were employed to obtain acceptable catalytic activity. The intimate mixture of iron and coal could then be drained of excess moisture, dried and subjected to hydrogenation or direct liquefaction of the coal. Prior workers also found the sulfide form of iron to be a more active hydrogenation catalyst.
Other prior workers have employed techniques in which water-soluble iron salts are impregnated into coal through contact with a solution of the salts. On subsequent drying with the gradual removal of water from the coal surfaces, the water-soluble, iron salt migrates into ever smaller water droplets resulting in the crystallization or precipitation of large particles of iron oxide. The inability to retard particle growth resulted in the requirement for high concentrations of iron when impregnated iron precursors were used as coal liquefaction catalysts.